Welcome to the forum! There will be bypass valve(s) on the rear of the water heater that need to be positioned, so you're not filling it with 6 gallons of antifreeze. There may be one, two, or three valves depending on how they built your unit. The heater should be bypassed with the valve(s), then drained via the plug at the lower left portion, accessible from the outside access door. Probably a plastic plug. Sorry, but no help on the filter question. Someone that's familiar with yours will post in.
Every day's a learning experience, though sometimes not what we expected.
2012 Jay Flight 19RD
2016 Ford F150 XLT 2X4 SC 3.5L Eco Max Tow
2010 Tundra TRD DBL Cab (Traded)
1 Spoiled Dog